Light Sensing Lamp

I have created a project which functions as a Light Detection Circuit, the "Light Sensing Lamp". It works using an LDR to detect darkness within the surrounding area, the end result being a circuit which lights up when dark. This aims to automate the process of switching a lamp on and off. For example, as it turns dark later in the day, the sensor would detect that darkness; turning the LED on effortlessly.

350Ω Resistor (340 in my version)

1kΩ Resistor

5mm White LED

100k Potentiometer

Light Detection Resistor (LDR)

9v Battery

9v Battery Holder

40x60mm Perf-board

3904 NPN Transistor

(Optional)

Breadboard kit

When starting off, Tinkercad is one of the best ways to test and design your circuit. It allows you to virtually create and simulate your circuit, allowing you to alter it while avoiding any wastage of materials. Furthermore, it lets you make any adjustments as needed, which was crucial when originally designing my circuit.

As you can see, my LED was short circuiting due to an excess amount of power. Using a multimeter, I was able to measure the voltage reaching it revealing that it was receiving too much voltage. My LED requires 2v, and I was using a 9v battery, this means that I would need a drop of 7v. To reduce it I would need to add a resistor using the calculation V = I x R, when substituted is 7(v)/0.02 (Due to it being a 20mA LED).

This way I was able to add a 350 Ω resistor.

Next is to ensure that the Circuit functions as intended, we can do this through the "Start Simulation" button on Tinkercad. Through this we can ensure 2 conditions:

When the LDR detects light, the LED is off.

When the LDR does not detect light, the LED is on.

The first step is to transfer your circuit to a physical breadboard. However, if you are an experienced electronics user, you may opt to skip this step. The breadboard is a solderless, and reusable way to physically re-create your circuit while being able to easily switch components.

The breadboard is split into 4 different sections, the red and blue sides parallel on the sides represent the positive and negative power respectively.

This is then separated from the two main connection sections, where the power goes horizontally for 5 slots. This is due to each being interconnected, allowing for easy use by pushing the ends of the components into the holes.

The next goal is to create your circuit on perfboard, which is another type of circuit board with evenly spaced holes. Each hole is surrounded by a small copper pad and insulating material, allowing you to solder the components after inserting them. However, unlike a breadboard there are not pre-made connections, meaning your have to individually connect each component through soldering. Furthermore, an optional addition to the circuit would be a switch between the positive power line, allowing you to avoid any sort of unnecessary power usage.

------- Safety -------

When soldering, you need to ensure you are working under the proper safety procedures.

1. Work in a well ventilated area to clear solder fumes
2. Wear safety glasses to avoid any splashes of solder
3. Keep soldering iron on it's stand when not in use
4. Use helping hands to keep perfboard still and hands away
5. Keep the tip away from you at all times (it reaches temperatures of 400°C)
6. Take power source out when working

The next step would be to make a casing for the circuit, designing it through online modelling applications such as Fusion360. This step works to transform your circuit into an actual product, while providing a layer of protection to avoid any shifting or messing within the circuit.

Using Fusion360, you can make a casing with accurate measurements and specifications. This enables you to 3D print a casing which fits perfectly with your circuit. This is perfect for the light circuit, it allows you to customise your build to follow designated purposes, for me (linked below) I was able to modify a cutout to include a switch.

Finally, it's time to 3D print your product! Either you could use the attached file, or use Fusion360 to modify/create a new casing that works for you.

A light detection circuit can be quite complicated, and its important to be able to understand your product.

To start, understanding the simple functions of the components is vital, first would be the battery which provides power in the form of positive and negative charge. Next would be a Light Detection Resistor (LDR), it has a high resistance which limits current but becomes low when it detects light. Another vital component would be the transistor, once the base pin receives enough power, it activates allowing power to flow through the collector and out the emitter. Next is the potentiometer, this is a type of resistor which weakens/strengthens depending on the dial which you can set. Another minor yet important part is the resistor, a resistor which always stays constant. Finally, would be the LED which in this case needs 2v to activate.

Now for the important part, how does the circuit work?

1. First the positive power goes through the potentiometer and LED
2. Then the power is split between two ways, the LDR and the resistor which connects to the Transistor
3. When it's bright, the resistance is low meaning the power going to the transistor base isn't enough to activate it
4. When it's dark, the resistance is high meaning all the power goes to the transistor
5. Since the transistor base can activate, the power can go through the transistor collector, and is emitted
6. that power now reaches the ground (negative power) which completes the circuit

In short, when its dark the LDR has high resistance, allowing the transistor to activate and complete the circuit

Congrats! You have made a Light sensing lamp which switches on when it's dark. Hope this has helped you learn about this circuit and electronics overall! Let me know if there are any improvements, fixes, or just any general feedback.